The invention relates to a pneumatic pressure control means for the production of at least two different pressures in a load line by the use of adjustment means.
Conventionally different pressures are made available in a load line by switching over a three way valve between two supply lines, which carry the desired pressures.
Furthermore it is a customary practice to utilize jet pumps to produce vacuum, in the case of which a jet tube nozzle carrying a fluid under gage pressure injects such fluid into a principal flow duct. In the transition zone between the jet nozzle and the principal flow duct a branch flow duct is provided in which vacuum is produced owing to the high flow speed of the medium.
One object of the invention is to provide a simple means by which pressures with different levels may be produced in a connected load line.
The pressure differences required in the branch flow duct are produced by influencing the principal flow without a valve being necessary for this purpose. Since the back pressure is influenced without making physical contact, use is more particularly advantageous in cases where frequent and rapid changes in pressure are required. The back pressure means may for example be in the form of a counter pressure nozzle directed against the outlet flow opening, whose flow rate may be changed. The back pressure means may furthermore be in the form of slides able to be moved, for example perpendicularly to the principal flow duct. A particular advantage of the invention is that only one supply duct is required, which may be more readily laid and connected as a double line in a restricted space. This means that it is possible to arrange the control means close to the load so that the change in pressure may take place particularly rapidly.
The influence on flow may be for example so set that the flow speed in the principal duct is reduced and the vacuum effective in the branch flow duct is eliminated or, dependent on the size of the back pressure, is converted into gage pressure. In this respect it is an advantage for the principal flow duct to be designed so that it flares like a trumpet toward the outlet opening in order to achieve flow with a minimum resistance. The back pressure means may, for example, be usch as to be able to be set in only two functional positions so that the pressure control means is merely effective as a sort of two way valve. It is however also possible to provide a multi-stage setting or adjustment so as to have any desired number of output pressures.
A baffle-like choke may be actuated by a shifting movement toward the outlet flow opening or athwart same without any mutual contact occurring. This simplifies the mechanical actuation and function of the pneumatic operations and may take place without mechanical wear, the choke being mechanically simple in design and as regards its guide means.
Therefore, as a result of the present invention, it is possible to regulate the pressures required in fine steps and to adapt same to various different conditions of use.
A displacement measuring means further renders possible a rapid movement of the choke into a predetermined position with a correspondingly defined pressure in the load line.
A pressure sensor and a control make it possible for the pressure in the load line to be set precisely and contact in a manner independent from the flow rate.
Linear drives produce a high hold and setting force so that a rapid setting action on the choke and reliable holding in the set position is possible. A moving coil may for example be designed like a loudspeaker and be coupled with a diaphragm sealing off the coil space so that same may be filled with a damping liquid.
In the following the invention will be described in detail with reference to the embodiments illustrated in accompanying drawings.